The present invention relates generally to multi-speed transmissions and more particularly to shift mechanisms for selectively engaging gears of these transmissions.
The development of manual shift multi-speed transmissions has created the problem of providing a shift mechanism which is capable of effecting all of the required transmission gear shifts while maintaining a relatively simple shift pattern. Shift mechanisms generally include a pivotable shift lever and may include a series of linkages operatively connected with the shift lever and adapted to engage and disengage gears of an associated transmission.
Conventional multi-speed transmissions utilize shift forks to axially drive gears into engagement, with each shift fork capable of engaging two gears. A plurality of shift forks is therefore required in a transmission having more than two speeds. Each shift fork is affixed to an axially slidable shift rod, with all of the shift rods of the transmission being adjacent and parallel. Most shift forks have a lug for driving engagement with the shifting mechanism. When all gears are in a neutral position, the lugs of each shift fork are generally laterally aligned with each other. The shifting mechanism must be capable of selectively engaging each of the shift fork lugs to drive each shift fork.
In some vehicles the driver's or operator's compartment is crowded and the need for a simple shift pattern becomes more pronounced. For example, in many heavy duty trucks the driver's compartment is located directly over the engine, with the engine projecting upward above the floor level of the compartment. The portion of the engine which projects into the driver's compartment is enclosed by a heat and sound insulating cover located between the driver and passenger seats. A multi-speed transmission is operatively affixed to the rear or output portion of the engine at a location substantially behind the driver's seat. A remote control shifting mechanism is therefore utilized to effect a shifting of the transmission gears. The gear shift lever normally used in these heavy duty trucks projects upward from the floor of the driver's compartment between the driver's seat and the engine cover. Shift levers of this type are conventionally pivotable in a forward and backward direction and in a sideways or lateral direction. A lateral pivoting of the shift lever affectuates a selecting of the aligned shift forks of the associated transmission while a forward or backward pivoting drives a selected shift fork backward or forward, thereby selectively engaging or disengaging the gears associated with the shift fork.
The space problems in the driver's compartment become more evident as the number of gears in the transmission increases. More lateral pivoting of the shift lever is required as more shift forks are used in the transmission. Obstruction of lateral movement of the shift lever by the driver's seat or the engine cover becomes an increased possibility.
In other types of vehicles such as smaller trucks or passenger cars, the transmission is located directly under the driver's compartment and a remote control shift mechanism is not required. The shift lever may extend from a direct control shift mechanism mounted on the transmission or may extend directly from the shift forks within the transmission. However, in either situation, sideways or lateral pivoting of the shift lever has heretofore been required to select one of a plurality of shift forks within the associated transmission. Seats or other equipment within the driver's compartment may obstruct or interfere with the lateral or side movement of the shift lever.